Using DataContext inside custom control - wpf

Question

I have a custom control with a ContentTemplate to display child controls. The data context isn't passing through my DataTemplate and so when I bind my child control, I'm not able to retrieve that value. I'm pretty sure that I'm not implementing this correctly specifically with respect to the DataTemplate, so I would appreciate any help. I've broken the problem down into as small a scenario as I can.
First, the Page:
<Window x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:WpfApplication1"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<ResourceDictionary>
<local:MainWindowViewModel x:Key="ViewModel" />
</ResourceDictionary>
</Window.Resources>
<Grid DataContext="{StaticResource ViewModel}">
<local:MyControl>
<local:MyControl.MainContent>
<DataTemplate>
<TextBlock Text="{Binding TextValue}" />
</DataTemplate>
</local:MyControl.MainContent>
</local:MyControl>
</Grid>
Next, the ViewModel:
Public Class MainWindowViewModel
Implements INotifyPropertyChanged
Public Event PropertyChanged(ByVal sender As Object, ByVal e As System.ComponentModel.PropertyChangedEventArgs) Implements System.ComponentModel.INotifyPropertyChanged.PropertyChanged
Private _textValue As String
Public Property TextValue() As String
Get
If String.IsNullOrEmpty(_textValue) Then
_textValue = "A default value"
End If
Return _textValue
End Get
Set(ByVal value As String)
_textValue = value
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("TextValue"))
End Set
End Property
End Class
And now my custom control code-behind:
Public Class MyControl
Inherits System.Windows.Controls.Control
Shared Sub New()
DefaultStyleKeyProperty.OverrideMetadata(GetType(MyControl), New FrameworkPropertyMetadata(GetType(MyControl)))
End Sub
Public Property MainContent As DataTemplate
Get
Return GetValue(MainContentProperty)
End Get
Set(ByVal value As DataTemplate)
SetValue(MainContentProperty, value)
End Set
End Property
Public Shared ReadOnly MainContentProperty As DependencyProperty = _
DependencyProperty.Register("MainContent", _
GetType(DataTemplate), GetType(MyControl), _
New FrameworkPropertyMetadata(Nothing))
End Class
And finally, my custom control definition:
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:WpfApplication1">
<Style TargetType="{x:Type local:MyControl}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type local:MyControl}">
<StackPanel>
<TextBlock Text="Hello, World!" />
<ContentControl x:Name="MainContentArea" ContentTemplate="{TemplateBinding MainContent}" />
</StackPanel>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
When this is run, the value from the ViewModel (TextValue) is not bound.

Answer 1

ContentControl is a little special in regards to DataContext. The DataContext within the DataTemplate is the Content of the ContentControl and not its DataContext. I didn't try your code but after a quick look I have a feelings that's your problem
You could try to bind the Content of the ContentControl to its DataContext with
<ContentControl x:Name="MainContentArea" Content="{Binding}" ...